Inkjet printers eject drops of ink through an array of nozzles to effect printing on a media substrate. The nozzles are typically formed on a silicon wafer substrate using semiconductor fabrication techniques. Each nozzle is a MEMS (micro electro-mechanical systems) device driven by associated drive circuitry formed on the same silicon wafer substrate. The MEMS nozzle devices and associated drive circuitry formed on a single nozzle is commonly referred to as a printhead integrated circuit (IC).
Some inkjet printheads have a single printhead IC. These are scanning type printheads that traverse back and forth across the width of a page as the printer indexes the length of the page past the printhead. The Applicant has developed a range of pagewidth printheads that have a nozzle array as long as the printing width of the page. These printheads remain stationary in the printer as the page is fed past. This allows much higher print speeds but is more complicated in terms of controlling the operation of a much larger array of nozzles.
The pagewidth array of nozzles is made up of a series of separate printhead IC's placed end to end. Skilled workers in this field will appreciate that more printhead IC's can be fabricated on the unprocessed circular silicon wafers if each IC is short rather than long. Furthermore, localized fabrication defects can render an entire printhead IC defective. Hence there is less chance that each individual IC will be defective if they are shorter.
The print data for each printhead IC in the pagewidth array of nozzles, is generated by another microprocessor in the printer, often referred to as a print engine controller (PEC). The PEC needs to be able to uniquely identify each of the printhead IC's so that it can send the correct print data to each nozzle. Therefore, each printhead IC has a unique address, called its write address that the PEC uses when it wants to send data to the drive circuitry on that particular IC.
The Applicant has found that it is beneficial to provide the pagewidth printhead in the form of a replaceable cartridge. If nozzle clogging or actuator burn out reduce the print quality to an unacceptable level, the user simply replaces the printhead instead of the entire printer. However, user expectation demands that the printhead replacement process be as simple and failsafe as possible. Therefore, the number of interconnections between the PEC and the printhead should be minimized.
When a replacement printhead is first installed, the PEC needs to interrogate the printhead IC's to determine their unique addresses so it can properly distribute the print data. This requires an electrical connection that is subsequently not used during normal operation of the printhead.